On Sat, Sep 19, 2020 at 11:50 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > > First of all, sorry for the horribly big Cc list! > > Following up to the discussion in: > > https://lore.kernel.org/r/20200914204209.256266093@xxxxxxxxxxxxx > > this provides a preemptible variant of kmap_atomic & related > interfaces. This is achieved by: > > - Consolidating all kmap atomic implementations in generic code > > - Switching from per CPU storage of the kmap index to a per task storage > > - Adding a pteval array to the per task storage which contains the ptevals > of the currently active temporary kmaps > > - Adding context switch code which checks whether the outgoing or the > incoming task has active temporary kmaps. If so, the outgoing task's > kmaps are removed and the incoming task's kmaps are restored. > > - Adding new interfaces k[un]map_temporary*() which are not disabling > preemption and can be called from any context (except NMI). > > Contrary to kmap() which provides preemptible and "persistant" mappings, > these interfaces are meant to replace the temporary mappings provided by > kmap_atomic*() today. > > This allows to get rid of conditional mapping choices and allows to have > preemptible short term mappings on 64bit which are today enforced to be > non-preemptible due to the highmem constraints. It clearly puts overhead on > the highmem users, but highmem is slow anyway. > > This is not a wholesale conversion which makes kmap_atomic magically > preemptible because there might be usage sites which rely on the implicit > preempt disable. So this needs to be done on a case by case basis and the > call sites converted to kmap_temporary. > > Note, that this is only lightly tested on X86 and completely untested on > all other architectures. > > The lot is also available from > > git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git highmem I think it should be the case, but I want to double check: Will copy_*_user be allowed within a kmap_temporary section? This would allow us to ditch an absolute pile of slowpaths. -Daniel > > Thanks, > > tglx > --- > a/arch/arm/mm/highmem.c | 121 --------------------- > a/arch/microblaze/mm/highmem.c | 78 ------------- > a/arch/nds32/mm/highmem.c | 48 -------- > a/arch/powerpc/mm/highmem.c | 67 ----------- > a/arch/sparc/mm/highmem.c | 115 -------------------- > arch/arc/Kconfig | 1 > arch/arc/include/asm/highmem.h | 8 + > arch/arc/mm/highmem.c | 44 ------- > arch/arm/Kconfig | 1 > arch/arm/include/asm/highmem.h | 30 +++-- > arch/arm/mm/Makefile | 1 > arch/csky/Kconfig | 1 > arch/csky/include/asm/highmem.h | 4 > arch/csky/mm/highmem.c | 75 ------------- > arch/microblaze/Kconfig | 1 > arch/microblaze/include/asm/highmem.h | 6 - > arch/microblaze/mm/Makefile | 1 > arch/microblaze/mm/init.c | 6 - > arch/mips/Kconfig | 1 > arch/mips/include/asm/highmem.h | 4 > arch/mips/mm/highmem.c | 77 ------------- > arch/mips/mm/init.c | 3 > arch/nds32/Kconfig.cpu | 1 > arch/nds32/include/asm/highmem.h | 21 ++- > arch/nds32/mm/Makefile | 1 > arch/powerpc/Kconfig | 1 > arch/powerpc/include/asm/highmem.h | 6 - > arch/powerpc/mm/Makefile | 1 > arch/powerpc/mm/mem.c | 7 - > arch/sparc/Kconfig | 1 > arch/sparc/include/asm/highmem.h | 7 - > arch/sparc/mm/Makefile | 3 > arch/sparc/mm/srmmu.c | 2 > arch/x86/include/asm/fixmap.h | 1 > arch/x86/include/asm/highmem.h | 12 +- > arch/x86/include/asm/iomap.h | 29 +++-- > arch/x86/mm/highmem_32.c | 59 ---------- > arch/x86/mm/init_32.c | 15 -- > arch/x86/mm/iomap_32.c | 57 ---------- > arch/xtensa/Kconfig | 1 > arch/xtensa/include/asm/highmem.h | 9 + > arch/xtensa/mm/highmem.c | 44 ------- > b/arch/x86/Kconfig | 3 > include/linux/highmem.h | 141 +++++++++++++++--------- > include/linux/io-mapping.h | 2 > include/linux/sched.h | 9 + > kernel/sched/core.c | 10 + > mm/Kconfig | 3 > mm/highmem.c | 192 ++++++++++++++++++++++++++++++++-- > 49 files changed, 422 insertions(+), 909 deletions(-) -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
